The subject invention pertains to ethylene polymers having an ultra-low molecular weight, as evidenced by a low number average molecular weight. In particular, the subject invention pertains to ethylene polymers having a number average molecular weight as determined by gel permeation chromatography of no more than 11,000.
U.S. Pat. No. 3,645,992, incorporated by reference herein in its entirety, discloses homogeneous linear ethylene olefin copolymers prepared using a soluble vanadium catalyst. Therein, homogeneous copolymers are defined as polymers in which the comonomer is randomly distributed within a given molecule, and in which all copolymer molecules have the same ethylene to copolymer ratio. The disclosed homogeneous copolymers have a moderately high molecular weight. For instance, as set forth in the Examples, the homogeneous copolymers have a melt index, as measured in accordance with ASTM D-1238, of from less than 0.1 to less than 25 g/10 min.
U.S. Pat. Nos. 5,272,236 and 5,278,272, incorporated by reference herein in their entirety, disclose substantially linear ethylene olefin copolymers prepared using a single site polymerization catalyst. The disclosed substantially linear copolymers are characterized as having from about 0.01 to about 3 long chain branches per 1000 carbons. Unlike the homogeneous copolymers of Elston, the disclosed substantially linear copolymers are characterized by a molecular weight distribution (Mw/Mn) which is independent of the I10/I2, as measured in accordance with ASTM D-1238.
Pourable ultra-low molecular weight ethylene polymers for use as oil additives are known in the art. For instance, PCT published application 93/12193 discloses ethylene/butene copolymers having a number average molecular weight between 1500 and 7500 prepared using a biscyclopentadienyl metallocene catalyst. Such polymers are said to exhibit a pour point of xe2x88x9230xc2x0 C. or less, as determined by ASTM Method No. D97. As set forth in the published application, polymers exhibiting such low pour points do not adversely affect the pour point of a lubricant to which they are added.
Non-pourable ethylene polymers having a narrow molecular weight distribution, i.e., an Mw/Mn less than 2.5, and an ultra-low molecular weight, as evidenced by a number average molecular weight (Mn) of no more than 11,000, have been heretofore unknown. Industry would find advantage in such polymers for use in adhesive formulations, and as wax substitutes, ink modifiers, oil modifiers, viscosity modifiers, fibers, processing aids, sealants, caulks, etc.
Accordingly, the present invention further provides a non-pourable homogeneous ultra-low molecular weight ethylene polymer which is characterized as having a number average molecular weight (Mn), as determined by gel permeation chromatography, of no more than 11,000, and a molecular weight distribution (Mw/Mn), as determined by gel permeation chromatography, of from 1.5 to 2.5.
The present invention further provides a non-pourable homogeneous ultra-low molecular weight ethylene polymer having longer lamella and a greater degree of crystalline organization than corresponding higher molecular weight materials at an equivalent density. In one instance, the present invention provides a non-pourable homogeneous ultra-low molecular weight semicrystalline ethylene/xcex1-olefin interpolymer having a density less than 0.900 g/cm3 characterized as having lamella greater than 40 nanometers in length when viewed using transmission electron microscopy.
The present invention further provides a process for preparing the non-pourable homogeneous ultra-low molecular weight ethylene polymers of the invention comprising: reacting ethylene and at least one ethylenically unsaturated comonomer at a reaction temperature of at least 80xc2x0 C. in the presence of a constrained geometry catalyst to form a non-pourable homogeneous ultra-low molecular weight ethylene polymer which is characterized as having a number average molecular weight (Mn) of no more than 11,000, and a molecular weight distribution, Mw/Mn, as determined by gel permeation chromatography, of from 1.5 to 2.5.